They occur where a carbohydrate chain is associated with phospholipids on the exoplasmic surface of the cellmembrane. The carbohydrates are found on the outer surface of all eukaryotic cell membranes. The carbohydrate structure of the glycolipid is controlled by the glycosyltransferases that add the lipids and glycosylhydrolases that modify the glycan after addition.
They extend from the phospholipid bilayer into the aqueous environment outside the cell where it acts as a recognition site for specific chemicals as well as helping to maintain the stability of the membrane and attaching cells to one another to form tissues.
Gangliosides (the most complex animal glycolipids; contain negatively charged oligosacchrides with one or more sialic acid residues; more than 200  different gangliosides have been identified; they are most abundant in nerve cells)
Glycophosphosphingolipids (complex glycophospholipids from fungi, including yeasts, and in plants, where they were originally called "phytoglycolipids" by Herbert Carter, et al., may comprise as complicated a set of compounds as the negatively charged gangliosides in animals. The head group of a glycolipid is composed of sugars.